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PREFACE, VII 
The fourth part consists of a paper by Mr. Henry Pittier on ‘‘The 
Mexican and Central American Species of Sapium.”’ 
During the past few years much study has been bestowed upon 
plants which furnish the rubber of commerce. This has shown that 
many of these are unknown botanically, that those which have been 
described have often been placed in wrong genera, and that the num- 
ber of genera and species which may furnish rubber is likely to prove 
much larger than has been supposed. It has been discovered not 
only that several species of the genus Sapium produce a part of the 
rubber of commerce, but that the genus is a very large one, and it 
will doubtless be found that more of its species are capable of yield- 
ing a satisfactory raw product. 
Mr. Pittier’s paper on the species of Sapium of Mexico and Central 
America is therefore, in view of the growing demand for rubber, 
timely, and the contents are such as to make it an important contri- 
bution to this subject. Most of the new species here proposed were 
first studied by Prof. Karl Schumann, but his death occurred before 
they had been published, or even manuscript upon them prepared. 
Mr. Pittier has described the new species recognized by Professor 
Schumann, together with two additional species distinguished by 
himself, and has added, with appropriate notes, descriptions of two 
already known. 
Part 5 consists of a paper, also by Mr. Pittier, on ‘‘ New and Note- 
worthy Plants of Colombia and Central America.’’ The plants 
considered were selected from several collections which have recently 
come into the possession of the United States National Museum. 
These collections form a most valuable addition to the herbarium, 
and their richness in new and rare species emphasizes the need of 
still further field work in tropical America and the more extensive 
study of the plants already collected. 
A second paper by A. S. Hitchcock, entitled ‘Catalogue of the 
Grasses of Cuba,” forms part 6 and is the result of an exhaustive 
study of the material in the United States National Herbarium and 
in the herbarium of the Estacién Central Agronémica de Cuba. It 
was chiefly through the efforts of Mr. Carl F. Baker, who obtained 
large collections in Cuba, that the specimens were made accessible 
to Mr. Hitchcock. It is hoped that this paper will be followed by 
similar ones upon other groups. 
In part 7 Dr. J. N. Rose continues his “Studies of Mexican and 
Central American Plants.’”’ This report varies little in style and 
treatment from the five numbers which have already been published. 
They all emphasize the botanical richness of the countries south of 
the United States, and the importance of careful work by experienced 
collectors. 
